1. Field
The present application relates generally to light emitting diodes, and more particularly, to gradient optics for controllable light distribution for LED light sources.
2. Background
A light emitting diode comprises a semiconductor material impregnated, or doped, with impurities. These impurities add “electrons” and “holes” to the semiconductor, which can move in the material relatively freely. Depending on the kind of impurity, a doped region of the semiconductor can have predominantly electrons or holes, and is referred to as an n-type or p-type semiconductor region, respectively.
In LED applications, an LED semiconductor chip includes an n-type semiconductor region and a p-type semiconductor region. A reverse electric field is created at the junction between the two regions, which causes the electrons and holes to move away from the junction to form an active region. When a forward voltage sufficient to overcome the reverse electric field is applied across the p-n junction, electrons and holes are forced into the active region and combine. When electrons combine with holes, they fall to lower energy levels and release energy in the form of light. The ability of LED semiconductors to emit light has allowed these semiconductors to be used in a variety of lighting devices. For example, LED semiconductors may be used in general lighting devices for interior or exterior applications.
A troffer is a light fixture resembling an inverted trough that is either recessed in, or suspended from, the ceiling. Troffers are typically designed to emit light using fluorescent lighting tubes. The fluorescent tubes emit light along the entire length of the troffer to produce a desirable light distribution pattern. Unfortunately, fluorescent lighting tubes may be expensive, require a warm up period, and produce flicker that people may find undesirable. Thus, LEDs are attractive candidates for replacing fluorescent lighting tubes in troffers. For example, LEDs have no warm up time, are long lasting and power efficient, and do not flicker. However, LEDs are considered to be a point light source in that the light is emitted from a relatively small region. Thus, utilizing LEDs in troffers present various design challenges since it is desirable to control how light emitted from an LED light source is distributed across the length of the troffer. One technique for using LEDs to obtain uniformly distributed light across the length of the troffer is to use a large number of LEDs that are distributed throughout the troffer. Unfortunately, this technique results in a complex troffer design and the cost of utilizing a large number of LEDs may be prohibitive.
Accordingly, what is needed is a simple and cost efficient way to provide controllable light distribution for use with point light sources thereby facilitating the use of LED semiconductors in troffer devices.